High strength light-framed wall structure

ABSTRACT

A light-framed wall structure contains a wall frame of studs, a bottom plate and a single top plate that together define a stud cavity; exterior sheathing attached to the wall frame and covering the stud cavity; and a polyurethane foam within the stud cavity and affixed to the exterior sheathing, studs, bottom plate and top plate.

CROSS REFERENCE STATEMENT

This application claims the benefit of U.S. Provisional Application No.61/364,413, filed Jul. 15, 2010, the entire content of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-framed wall structure, aprocess for making the light-framed wall structure and a buildingcontaining the light-framed wall structure.

2. Description of Related Art

There is a continuous drive in the building industry to decreasebuilding costs while increasing thermal insulating properties andmaintaining structural integrity under building codes. Wall framingmembers are one type of building element that plays a role in allaspects of this drive. The large number of framing members in alight-framed wall structure inherently makes them a notable contributorto the building cost. Framing members also have a relatively lowinsulation value and serve as a means for thermal shorts through a wallstructure since insulation is often applied only between the framingmembers. From a cost and insulation perspective, it would be desirableto reduce the number of framing members in a light-framed wallstructure.

However, building codes specify that wall structures must meet certainstructural integrity criteria. In particular, a wall in a buildingstructure must withstand lateral and transverse loads resulting fromwind and earthquakes as well as axial loads due to structure weight,snow, and floor loads. The International Residential Building Code (IRC)and International Building Code (IBC) provide prescriptive solutions andminimum standards for walls that meet code structural integritycriteria. The prescriptive solutions commonly utilize 2×4 studs spaced16-inch on center, or 2×6 studs spaced 24-inches on center, with adouble top plate over the studs to distribute axial point loads.Additionally, the IRC and IBC allow for a single top plate provided thatroof rafters or floor joists align within one inch of stud centerlinesso as to directly transfer their load to a stud below. While such a walldesign reduces building elements by using a single top plate, thenecessary careful alignment of roof rafters or floor joists reducesflexibility in building designs and construction. The IRC and IBC allowfor custom engineered wall designs provided the wall has sufficient loadbearing properties.

It is desirable to develop a light-framed wall structure that cansupport axial point, transverse and lateral loads sufficiently to meetIRC and IBC requirements for structural integrity but by using fewerframing members, especially if such a wall structure requires only asingle top plate and alignment of second floor studs and/or roof raftersand trusses did not have to align within one inch of the wall structurestuds. Even more desirable is such a light-framed wall structure thatwould eliminate the problem of thermal shorts through the wall caused bythe studs by including an insulating layer that extends over the studs.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a solution to the desire for alight-framed wall structure that can support axial point, transverse andlateral loads sufficiently to meet IRC and IBC requirements forstructural integrity with fewer framing members and in particular such awall structure requiring only a single top plate where alignment ofsecond floor studs and/or roof rafters and roof trusses do not have toalign within one inch of the wall structure studs. Even more, thepresent invention can provide a light-framed wall structure thateliminates thermal shorts through the wall caused by the framingelements by including an insulating layer that extends over the studs.

Surprisingly, the objectives of the present invention are achievablewith a stud spacing in a range of nominally 16 inches to nominally 24inches on center, even when using a single top plate, sheathingoverlaying the studs and spanning the spacing between the studs and thepresence of polyurethane foam disposed in the stud cavity adhering tothe studs and the sheathing.

Light-framed wall structures of the present invention surprisingly canconcomitantly support (that is, withstand; resist without failure) axialpoint loads of 2500 pounds or more, even 3500 pounds or more, and even4000 pounds or more (and desirably uplift loads of 1500 pounds or moreeven 2000 pounds or more) according to ASTM method E72, Section 9 asmodified in the Example below (exclusion of the I-beam along the topplate); lateral loads of 500 pounds per linear foot (plf) or more, even750 plf or more, and even 1000 plf or more according to ASTM method E72,Section 14; and transverse loads of 150 pounds per square foot (psf) ormore, even 200 psf or more, and even 250 psf or more according to ASTMmethod E72, Section 11.

In a first aspect, the present invention is a light-framed wallstructure comprising: (a) studs spaced apart from one another in a rangeof nominally 16 to nominally 24 inches on center; (b) a bottom plate anda single top plate spanning the studs and attached to opposing ends ofthe studs such that the studs, top plate and bottom plate define a wallframe having opposing interior and exterior surfaces with the studs, topand bottom plate further defining a stud cavity within the wall frame,the stud cavity having a height extending from bottom plate to top plateand a width extending from one stud to another stud; (c) sheathingspanning the width and height of the stud cavity and overlapping thestuds and attached to at least one of the exterior and interior surfacesof the wall frame; and (d) polyurethane foam forming a seal around theinside perimeter of the stud cavity and affixed to the sheathingmaterial on at least one surface of the wall frame, the stud, top plateand bottom plate where the polyurethane foam extends at least 1.5 inchesover the sheathing, studs, top plate and bottom plate along theperimeter and further is present at an average thickness of at least 3.5inches over the volume of the stud cavity within six inches of the topplate; wherein the light-framed wall structure is free of metal cornerconnectors or reinforcements comprising a box-shaped section againstwhich the studs, bottom plate and top plate abut.

In a second aspect, the present invention is a light-framed wallstructure comprising: (a) studs nominally spaced apart from one another24 inches on center; (b) a bottom plate and a single top plate spanningthe studs and attached to opposing ends of the studs such that thestuds, top plate and bottom plate define a wall frame having opposinginterior and exterior surfaces with the studs, top and bottom platefurther defining a stud cavity within the wall frame, the stud cavityhaving a height extending from bottom plate to top plate and a widthextending from one stud to another stud; (c) exterior sheathing spanningthe width and height of the stud cavity and overlapping the studs andattached to the exterior surface of the wall frame; and (d) polyurethanefoam within the stud cavity and affixed to the exterior sheathingmaterial, studs, top plate and bottom plate defining the stud cavity,the polyurethane foam having an average thickness of at least 0.5 incheswithin the stud cavity; wherein the light-framed wall structure is freeof metal corner connectors or reinforcements comprising a box-shapedsection against which the studs, bottom plate and top plate abut.

In a third aspect, the present invention is a process for making thelight-framed wall structure of the first aspect, the process comprisingthe following steps: (a) assembling studs nominally spaced 24 inches oncenter between a single top plate and a bottom plate so as to form awall frame having opposing interior and exterior surfaces and defining astud cavity between the studs and top and bottom plates and affixing thestuds to the top and bottom plates; (b) affixing exterior sheathing tothe exterior surface of the wall frame over the studs and stud cavity;and (c) disposing a polyurethane foam into the stud cavity onto theexterior sheathing and against the studs and top and bottom plates so asto have an average expanded thickness of at least 0.5 inches within thestud cavity and so that the polyurethane foam attaches to the exteriorsheathing, studs and top and bottom plates of the stud cavity.

In a fourth aspect, the present invention is a building structurecomprising the light-framed wall structure of the first aspect.

The light-framed wall structure and process of the present invention isuseful in constructing buildings. The building of the present inventionis useful as a building structure for many types of use includingresidential housing and light commercial buildings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of the light-framed wall structure ofpresent invention with FIG. 1(A) illustrating a cutaway view lookingdown from the top from under the top plate and FIG. 1(B) illustrating aview from the interior surface side.

FIG. 2 illustrates an embodiment of the light-framed wall structure ofthe present invention illustrating a view from the interior surfaceside.

DETAILED DESCRIPTION OF THE INVENTION

“ASTM” refers to American Society for Testing and Materials and is usedto designate a test method by number as published by ASTM. Test numbersrefer to the most recent test published prior to the priority date ofthis document unless otherwise specified by a date using a hyphenatedsuffix after the test number.

“Multiple” means two or more. “And/or” means “and, or as analternative”. All ranges include endpoints unless otherwise indicated.

“Length”, “width” and “thickness” are three mutually perpendiculardimensions of an object. Length is a dimension having a magnitudeequivalent to the largest magnitude dimension of the length, width andthickness. Thickness has a magnitude equal to the smallest magnitude ofthe length, width and thickness. Width has a magnitude equal to thelength, thickness, both the length and thickness, or a magnitudesomewhere between that of the length and thickness.

“Light-framed wall structure” refers to a wall structure comprisingstuds spaced apart from one another and attached at opposing ends to topplate and bottom plate members. The studs, top plate and bottom platedefine a wall frame that defines stud cavities between studs and the topand bottom plates.

“Polyurethane foam” refers to a polymeric foam wherein the polymericmatrix of the foam comprises polyurethane linkages formed by reactingisocyanate functionalities with polyol and/or other reactive additives.The polyurethane foam has an isocyanate index in a range of 95 orhigher, preferably 100 or higher, still more preferably 120 or higherand yet more preferably 150 or higher. At the same time the isocyanateindex is desirably 350 or lower, preferably 300 or lower, morepreferably 250 or loser and yet more preferably 200 or lower. Determineisocyanate index by multiplying 100 times the actual amount ofisocyanate used divided by the theoretical amount of isocyanate requiredto stoichiometrically react with all of the polyol and otherisocyanate-reactive additives in the foam formulation.

In one aspect the present invention is a light-framed wall structure. Inthe light-framed wall structure of the present invention the studs arespaced apart nominally 16 to 24 inches on center. Particularly commonspacings suitable for use in the present invention include nominally 16inches on center, nominally 19.2 inches on center and nominally 24inches on center. “Nominal” values include tolerances from the specificvalue that are commonly accepted in the construction industry. Forexample, actual spacing can be off from a nominal value by as much as0.125 inches or less, preferably 0.0625 or less, more preferably 0.0312inches or less from being spaced exactly the nominal value. Spacing “oncenter” refers to a measurement taken from the center of one stud to thecenter of the next neighboring stud. Typically, studs are aligned suchthat the surface of one stud faces the surface of another stud and thedistance on center is measured from the center of the thickness (centerof an edge) of one stud to the center of the thickness (center of anedge) on a neighboring stud.

Studs can be any stud known or yet to be used in constructinglight-framed wall structures. Suitable studs include what is commonlyknown as 2×4 and/or 2×6 dimensional building elements, where the numbersdesignate the nominal thickness and width of the building elements ininches rounded up to the nearest inch. Typically, 2×4 elements arenominally 1.5 inches thick and nominally 3.5 inches wide and 2×6elements are nominally 1.5 inches thick and nominally 5.5 inches wide.Often studs are made from lumber (wood) or metal (typically, thin gaugesteel). Studs, as well as top and bottom plates, have opposing surfaces,edges and ends. The width of a stud and bottom plate separates opposingedges, thickness separates opposing surfaces and length separatesopposing ends.

The light-framed wall structure of the present invention is furthercharacterized by having a bottom plate and a single top plate, eachspanning multiple studs. Bottom plates and top plates can be anycurrently known or yet to be developed material for light-framed wallstructures. As with the studs, the bottom plate and top plate are oftendimensional building elements such as 2×4 or 2×6 materials. It is commonto use dimensional building elements of the same thickness and width forthe top plate, bottom plate, or both top plate and bottom plate as isused for the studs they span. It is also common to use top and bottomplates made of the same material as the studs they span.

As the name suggests, bottom plates and top plates span the bottom andtop of the studs, respectively, to form the wall frame of thelight-framed wall structure. Studs have one of their ends attached to asurface of a bottom plate and their opposing end attached to a surfaceof a top plate. It is common to attach the studs to the top and bottomplates using nails (for example, steel nails) when the building elementsare wood and screws or pins when the building elements are metal. Insuch a configuration, neighboring studs and the top and bottom platesspanning those studs define a stud cavity having a height extending fromthe bottom plate to the top plate (the length of the studs) and a widthextending from one stud to a neighboring stud. It is common for thestuds to have an orientation in the light-framed wall structure suchthat the surface of one stud faces the surface of a neighboring stud andthe facing surfaces are both exposed within a stud cavity. At the sametime, one of the edges of each stud (the inside edge) is on what shallbe called the “interior” surface of the wall frame and the opposing edgeof the stud (the outside edge) is on what shall be called the “exterior”surface of the wall frame. Similarly, a surface of the top plate faces asurface of the bottom plate and both of these facing surfaces areexposed within a stud cavity while one of the edges of each of the topand bottom plates is on the interior surface of the wall frame and theopposing edge is on the exterior surface of the wall frame.

The wall frame achieves sufficient strength without requiring metalcorner connectors having box-shaped intermediate sections as taught inU.S. Pat. No. 7,882,666 ('666). Reference '666 discloses a prefabricatedbuilding component that comprises a frame of lumber components in arectangular orientation and joined together with metal cornerconnectors. Each corner connector comprises a metal box against whichthe lumber components abut. These corner reinforcements are necessarycomponents of the '666 structure. However, the present invention is freeof metal corner connector having box-shaped intermediate sectionsagainst which the studs, top plate and bottom plate abut. Applicantshave discovered a method of achieving suitable strength, particularlyracking strength, with the wall structure of the present inventionwithout requiring such metal corner reinforcements.

As noted, the wall frame has a stud cavity defined therein. Whileteachings, including descriptions and claims, herein generally refer to“a” stud cavity defined within a wall frame by studs, top and bottomplates, the wall frame can and typically does have multiple studcavities defined by the studs, top and bottom plates of the wall frame.The wall frame of the light-framed wall structure of the presentinvention can have defined therein one or more than one stud cavity(that is, reference to “a” stud cavity does not imply there is only asingle stud cavity in the wall frame). Teachings herein, when referringto “a” stud cavity, can and desirably do apply to more than one and mostdesirably apply to each stud cavity in a wall frame of the light-framedwall structure when the light-framed wall structure has multiple studcavities defined therein. For example, teaching that exterior sheathingfully covers the stud cavity should be understood as meaning exteriorsheathing preferably fully covers multiple stud cavities if the wallframe contains more than one stud cavity, and more preferably coverseach stud cavity of the wall frame. Similarly, teaching aboutpolyurethane within a stud cavity should be understood as desirablybeing applicable to multiple and preferably each stud cavity of the wallframe when the wall frame contains more than one stud cavity.

Wall frames can also have defined therein sub-cavities within a studcavity. A sub-cavity is a portion of a stud cavity that does not extendfrom a base plate to a top plate. For example, headers and sillsextending from one stud to a neighboring stud divide a stud cavity intomultiple sub-cavities for framing a window into a wall frame. One of thesub-cavities is sized to accommodate the window and is not filled withpolyurethane foam or covered with exterior or interior sheathing.However, the sub-cavities that are typically above and/or below thewindow are desirably treated as described herein for a stud cavity inthe present invention—that is, the sub-cavities are covered withsheathing and polyurethane foam disposed within the sub-cavity and,generally, enclosed with both exterior and interior sheathing. In likemanner, framing for a door in a wall frame can result in creation ofseparate sub-cavities of a stud cavity, one to fit the door and theother to be desirably treated in like manner as a cavity of the presentinvention. It is desirable to treat sub-cavities as stud cavitiesaccording to the teachings herein in order to achieve an optimallyinsulated and reinforced wall structure of the present invention, exceptfor those sub-cavities that accommodate a functional component such as adoor or window.

The light-framed wall structure of present invention comprises sheathingthat spans the width and height of the stud cavity thereby covering(typically, entirely covering) the stud cavity and overlapping the studsof the wall frame. The sheathing overlaps and attaches to edges of thestuds on a surface of the wall frame. The sheathing can be exteriorsheathing attached to the exterior surface of the wall frame, interiorsheathing attached to the interior surface of the wall frame, or thelight-framed wall structure can comprise both exterior and interiorsheathing attached to their corresponding surfaces of the light-framedwall. It is desirable that the light-framed wall structure comprise atleast exterior sheathing. Exterior sheathing serves as a protectivebarrier from outside elements and can further serves as thermalinsulation as well as structural reinforcement

Suitable sheathing includes panels of foam sheathing (for example,polymeric foam board that can comprise facer material on one or morethan one surface or that is free of facer material), wood sheathing (forexample, oriented strand board or plywood), fibrous structural board(for example, fiberboard), composite structures such as structuralinsulated sheathing, gypsum board, or paneling of any composition.Typically, exterior sheathing is selected from foam sheathing, woodsheathing, fibrous structural board, gypsum board and compositionstructures such as structural insulated sheathing. Typically, interiorsheathing is selected form gypsum board and paneling. Gypsum boardrefers to what is also known as drywall or plasterboard.

Desirably, the present invention includes exterior sheathing. Even moredesirably, the exterior sheathing simultaneously increases structuralintegrity, barrier properties and thermal insulation to the light-framedwall structure. In that regard, particularly desirable exteriorsheathing comprises an insulating foam element and a structuralsheathing element such as wood sheathing or fibrous sheathing in asingle product that can be applied onto a wall frame in a single step.Such a product is commonly referred to as structural insulated sheathing(SIS). A SIS product provides a combination of thermal insulation, waterand air barrier properties and structural strength to the light-framedwall structure of the present invention. An example of a particularlydesirable exterior sheathing that provides a combination of structuralintegrity, barrier properties and thermal insulation in a singlesheathing material is STYROFOAM SIS™ Brand Structural InsulatingSheathing (STYROFOAM SIS is a trademark of The Dow Chemical Company).ZIP insulated system sheathing is also suitable (available from HuberEngineered Woods LLC) that provides structural integrity, barrierproperties and thermal insulation together in a single sheathingmaterial.

Use of thermally insulating exterior sheathing, such as SIS orinsulating foam panels, in the present invention results in a thermallyinsulating layer that completely covers studs by overlaying the exteriorsurface of the wall frame. As a result, the thermally insulatingexterior sheathing precludes the studs from efficiently acting asthermal shorts through the light-framed wall structure. Reducing, eveneliminating studs from acting as thermal shorts through a wall providesa superior thermally insulated wall structure over more commonlight-framed wall structures containing thermal insulation only in studcavities.

The sheathing is attached to a surface of the wall frame by any meansnow known or yet to be discovered in the building industry. Examples ofsuitable means include any one or any combination of more than one ofthe following: mechanical fasteners (such as screws, pins, nails andstaples), liquid adhesives (such as caulks and glues), and foamadhesives (such as thermoset foams including polyurethane spray foam),and plasticized adhesives (such as hot-melt glue). It is desirable touse an adhesive to adhere the sheathing to the wall frame, either aloneor in combination with mechanical fasteners, with a continuous bead ofadhesive along the wall frame members. Maximizing the surface of thewall frame to which the sheathing attaches maximizes the mechanicalstrength of the resulting light-frame wall structure.

The stud cavity of the light-framed wall structure desirably containspolyurethane foam around the inside perimeter of a stud cavity andaffixed to the studs, top plate, bottom plate and sheathing (that is,affixed simultaneously to each of these wall structural elements). Thepolyurethane foam adjoins the building elements together around theinside perimeter of the stud cavity, joining the sheathing to the studs,top plate and bottom plate much like a fillet weld. The polyurethanefoam desirably extends a distance of at least 1.5-inches over the studs,top plate, bottom plate and sheathing around the inside of the perimeterof the stud cavity to ensure a good seal and strong structuralreinforcement of the wall structure. For optimal sealing performance andstructural integrity the polyurethane foam should be continuous aroundthe inside perimeter of the stud cavity. However, occasional breaks orspaces in the foam around the perimeter can be acceptable.

The polyurethane foam desirably has a greater expanded thicknessproximate to the top plate than on average within a stud cavity.Polyurethane foam proximate to the top plate can support and stabilizethe top plate from bending and twisting under load. Stabilization of thetop plate is achievable without requiring the same thickness ofpolyurethane foam throughout the stud cavity. Therefore, a costeffective way to stabilize the top plate is to dispose polyurethane foamto a thicker expanded thickness proximate to the top plate. Thepolyurethane foam is present at an average thickness of 3.5-incheswithin the volume of the stud cavity within six inches, preferablywithin eight inches, more preferably within ten inches of the top plate.Measure polyurethane foam thickness perpendicular to the sheathing towhich it is affixed.

To further increase thermal insulating properties of the wall it isdesirable that the spray polyurethane foam has an average expandedthickness of at least 0.5 inches within the stud cavity and desirablyhas an expanded thickness of at least one inch, preferably at least 1.5inches and more preferably at least two inches within the stud cavity.Measure the expanded thickness of the polyurethane foam perpendicular tothe sheathing to which the polyurethane is affixed. The polyurethanefoam provides thermal insulation to the light-framed wall structure aswell as additional structural reinforcement. By binding to the wallstructural elements the polyurethane foam reinforces those elements frommoving with respect to one another and, as such, provides strength tothe light-framed wall structure. Desirably, the polyurethane foamextends throughout the stud cavity and covers sheathing on at least onesurface of the wall frame that would otherwise be exposed within thestud cavity in order to provide thermal insulation, air and vaporbarrier properties and structural reinforcement throughout the entirestud cavity.

Polyurethane foam can, but does not necessarily, fill a stud cavity.Commonly, the thickness of the polyurethane foam is less than the widthof the stud and so there is still void space within a stud cavity.Moreover, electrical fixtures and wiring, plumbing pipes and the likecan exist within a stud cavity in combination with the polyurethanefoam. Polyurethane foam can be introduced into stud cavities before orafter installation of electrical components (fixture, wiring, and thelike) and/or plumbing components. Beneficially, the polyurethane foamcan expand within the stud cavity around the electrical and/or plumbingcomponents.

The polyurethane foam is desirably a spray-in-place (or simply “spray”)polyurethane foam. Spray polyurethane foam inherently attaches to wallstructural elements (studs, plates and sheathing) that it contacts as itcures. Application of spray polyurethane foam to a light-framed wallstructure can occur with the light-framed wall structure in anyorientation including a vertical orientation, such as is typically theorientation in a completed building structure. Spray polyurethane foamis becoming common in the construction industry as an insulatingmaterial. A desirable feature of spray polyurethane foam is that it canbe applied to a wall structure on the construction site or any timeprior to arriving at the construction site and to a wall structure inany orientation. Another desirable feature of spray polyurethane foam isthat it can be applied at a constant or a variable thickness within astud cavity. For example, the polyurethane foam can be applied thickerproximate to the top plate than on average within a stud cavity in orderto provide greater structural integrity proximate to the top plate.Spray polyurethane foam can be readily applied thicker proximate to thetop plate in order to achieve such a configuration. Measure polyurethanefoam thickness perpendicular to the sheathing material to which it isaffixed.

Other than spray-in-place polyurethane foams, pour-in-place polyurethanefoams are also suitable, particularly for prefabricated light-framedwall structures that are made remotely from the construction site anddelivered as a unitary structure to the construction site. As with spraypolyurethane foams, pour-in-place polyurethane foams inherently tend toadhere to the building elements they contact as they cure.

The polyurethane can have an open cell or closed cell structure, thoughclosed cell foam is generally preferred because it is often a betterthermal insulator and mechanically stronger foam. Closed cell foam hasan open cell content of 30% or less, preferably 20% or less, morepreferably 10% or less, still more preferably 5% or less and mostpreferably 1% or less according to ASTM method D-6226.

The polyurethane foam desirably has a density of 0.4 pounds per cubicfoot (pcf) or more, preferably 0.5 pcf or more or more and can be onepcf or more. At the same time, the polyurethane foam desirably has anexpanded density of 2.8 pcf or less, preferably 2.2 pcf or less and canbe 2.0 pcf of less. When the polyurethane foam has an expanded densitybelow 0.4 pcf it provides less than optimal structural reinforcement tothe light-framed wall structure. When the polyurethane foam expandeddensity exceeds 2.8 pcf a higher cost and reduction in thermalinsulation of the foam tends to outweigh an enhanced mechanicalstrength. Generally, open cell polyurethane foam is lower density foamthan closed cell foam. Open celled foam is commonly available asnominally 0.5 pcf foam and closed cell foam is commonly available asnominally two pcf foam.

Characteristic of the present invention is use of a single top plate incombination with a stud spacing in a range that is nominally 16-24inches on center. Yet the light-framed wall structure of the presentinvention surprisingly has the further characteristics of concomitantunexpectedly high axial point, lateral and transverse load bearingproperties. Light-framed wall structures of the present inventionsurprisingly can concomitantly support: (1) axial point loads of 2500pounds or more, even 3000 pounds or more according to ASTM method E72,Section 9 as modified in the Example below (exclusion of the I-beamalong the top plate); (2) lateral loads of 500 pounds per linear foot(plf) or more, even 750 plf or more, and even 1000 plf or more accordingto ASTM method E72, Section 14; and (3) transverse loads of 150 poundsper square foot (psf) or more, even 200 psf or more, and even 250 psf ormore according to ASTM method E72, Section 11.

Even with a single top plate and stud spacing of a nominal 24 inches oncenter, and even when using 2×4 studs with a single top plate and studspacing of a nominal 24 inches on center, wall structures of the presentinvention can achieve these demanding axial point load bearing valueswithout having to position the axial point load within one inch of astud, as the building codes presently specify. Such an achievement is avaluable advancement in the art by achieving prescribed structuralintegrity while reducing the framing factor of a structure. Reducing theframing factor corresponds to reducing the amount of a structure'ssurface area that corresponds to framing (for example, studs, topplates, and bottom plates). The framing can serve as thermal shortsthrough the walls of a building so reducing the framing factor of astructure allows for reduced thermal shorts through the wall of thestructure.

These surprising load bearing characteristics make the light-framed wallstructure of the present invention exceptionally desirable in thebuilding industry because the light-framed wall structure offersdesirably high mechanical integrity with versatility in placing loadsrelative to stud positions all while reducing the number of framingelements relative to common light-framed wall structure designs. Forexample, 2×4 studs with a nominal 24 inch spacing and with a single topplate can be used without requiring roof rafters or floor joints toalign within one inch of the studs of the present invention. Moreover,use of thermally insulating exterior sheathing provides efficientthermally insulating properties and reduces or minimizes thermal shortsthrough the light-framed wall structure caused by studs.

Another aspect of the present invention is a process for making thelight-framed wall structure of the present invention. The processcomprises assembling studs nominally spaced 24 inches on center betweena single top plate and a bottom plate so as to form a wall frame thatdefines stud cavities between the studs and the top and bottom platesand affixing the studs to the top and bottom plates; affixing asheathing onto a surface of the wall from over the studs and studcavities; and disposing a polyurethane foam into the stud cavity ontothe exterior sheathing and against the studs and top and bottom platesso as to have an average expanded thickness of at least two incheswithin the stud cavity and so that the polyurethane foam attaches to thesheathing, studs and top and bottom plates of the stud cavity. Theprocess can include applying and affixing sheathing to both the exteriorand the interior surfaces of the wall frame. Each of the buildingelements and various embodiments of the elements and structures for usein the process of the present invention are as described for the wallstructure of the present invention.

Yet another aspect of the present invention is a building structurecomprising the light-framed wall structure of the present invention. Thelight-framed wall structure of the present invention has utility as awall for a building structure. A building structure comprising thelight-framed wall structure of the present invention is not possibleapart from the light-framed wall structure of the present invention.Therefore, the building structure comprising the light-framed wallstructure of the present invention is yet another embodiment of thepresent invention.

The following Example serves to illustrate an embodiment of the presentinvention. Notably, transverse load values were not actually measuredbut are expected to exceed 200 psf based on prior testing of similarstructures with fewer components.

EXAMPLE 1 Absent Interior Sheathing

FIG. 1 illustrates two different views of light-framed wall structure 10of the present invention and Example in order to further facilitateunderstanding of the present invention.

Position two 2×4 dimensional lumber studs 20 that are 93 inches longbetween single 2×4 dimensional lumber top plate 30 and single 2×4dimensional lumber bottom plate 40 and spaced apart a nominal 24 incheson center. The 2×4 dimension lumber is 1.5 inches thick and 3.5 incheswide. Fasten studs 20 to the both top plate 30 and bottom plate 40 byusing two 3.5 inch long 0.162 inch diameter nails per stud to form anwall frame defining a stud cavity with one 3.5 inch wide surface fromeach of studs 20 and plates 30 and 40 facing the cavity. Attach to thewall frame exterior sheathing 50, a sheet of 0.5-inch thick STYROFOAMSIS™ Brand Structural Insulated Sheathing, so as to cover the studcavity from one side of the wall frame. Attach sheathing 50 to the wallframe using 7/16-inch crown by two-inch long 16 gauge staples.

Spray polyurethane foam 60 (for example, Dow Spray Foam 2045, availablefrom The Dow Chemical Company) into the stud cavity to an expandedthickness of at least two inches. Over the area within 6 inches of topplate 30 spray polyurethane foam 60 to an expanded thickness of 3.5inches. Cover any of sheathing 50 otherwise exposed in the stud cavitywith spray foam 60 and dispose spray foam 60 against studs 20 and plates30 and 40 around the perimeter of the stud cavity. Spray foam 60 expandsto an average density of 2.2 pcf.

Test the resulting light-framed wall structure 10 to a lateral load wallstrength test (ASTM E72, Section 14) and a modified axial point loadwall strength test (ASTM E72, Section 9). Modify the axial point loadwall strength test by excluding the I-beam spanning the stud cavity overtop plate 30. In other words, apply the axial point load directly ontotop plate 30 centrally between studs 20. This modification makes it moredifficult for light-framed wall structure 10 to support axial pointloads because the I-beam is not present to help distribute the load.Nonetheless, light-framed wall structure 10 performs remarkably well ineach of the lateral load wall strength test, transverse load test andthe modified axial point load wall strength test.

The Example light-framed wall structure 10 withstands lateral loads upto 1081 plf. For reference, a comparative code compliant light-framedwall structure with 2×4 studs 16 inches on center and using a double topplate with fiberglass insulation in the stud cavity and wood structuralpanel sheathing fasten with 0.113 shank diameter nails and 6 inches oncenter at the edges and 12 inches on center on non-edge studs, andcovering the exterior surface of the wall frame only bears up to 515 plfin the lateral load test.

The Example wall structure 10 withstands axial point load up to 3294pounds in the modified axial point load wall strength test.

This Example illustrates a light-framed wall structure of the presentinvention that can support remarkably high lateral, axial point andtransverse loads despite having a single top plate and 2×4 studspositioned a nominal 24 inches on center.

The performance of wall structure 10 would only improve (that is, loadvalues would stay the same or increase) with the inclusion of interiorsheathing. Hence, the surprising result of the strength of this wall isindependent of the type of interior sheathing that one might include tobring this example within scope of the present invention.

EXAMPLE 2 One-Inch SIS Exterior Sheathing

Prepare a wall structure similar to wall structure 10 of Example 1except use a one-inch thick SIS panel for the exterior sheathing 50 anda spray polyurethane foam to a thickness of at least one-and-one halfinches in the stud cavity while having an expanded thickness of 3.5inches entirely within ten inches (which inherently includes the firstsix inches) of top plate 30. Attach an interior sheathing to the wallframe on an opposite side to the SIS exterior sheathing so as to coverthe stud cavity from the inside of the wall frame. Use as interiorsheathing 0.5-inch thick gypsum wall board using number 6 screws everysixteen inches around the perimeter and interior of the board.

Test the resulting light-framed wall structure in like manner as thefirst example except use unrestrained ASTM E-2126 for testing lateralload wall strength. The “unrestrained” test format means that the wallis only anchored to a test base with ½-inch anchor bolts every six feetand not restrained with other hold-downs or tie down rods. The resultingwall structure has a capacity of 759 pounds per lineal foot under thelateral load test and 4031 pounds in the axial load wall test.

EXAMPLE 3 Wood Exterior Sheathing

Prepare a wall structure similar to wall structure 10 in Example 1except use as the exterior sheathing 7/16-inch thick grade PS2 24/0oriented strand board. Test the resulting light-framed wall structure inlike manner as wall structure 10 in Example 1.

The resulting wall structure has a capacity of 1422 pounds per linealfoot under the lateral load test; an excess of 200 psf in the transverseload test and 7348 pounds in the axial load wall test. As with Example1, addition of interior sheathing would not diminish these values and soincluding any interior sheathing to the structure of this example wouldhave at least these surprisingly high capacity values.

EXAMPLE 4 Gypsum Board Sheathing

Prepare a wall structure similar to wall structure 10 in Example 1except use as the sheathing ½-inch thick standard interior gypsum board.Test the resulting light-framed wall structure in like manner as thewall structure in Example 2.

The resulting wall structure has a capacity of 678 pounds per linealfoot under the lateral load test and 4262 pounds in the axial load walltest. Test results are expected to stay the same or increase if anothersheathing was included on an opposing side of the wall structure.

EXAMPLE 5 Extruded Polystyrene Foam Sheathing

Prepare a wall structure similar to wall structure in Example 2 exceptuse as the exterior sheathing one-inch thick extruded polystyrene foam(STYROFOAM™ Residential Sheathing, STYROFOAM is a trademark of The DowChemical Company). Test the resulting wall structure in like manner asthe wall structure in Example 2.

The resulting wall structure has a capacity of 490 pounds per linealfoot under the lateral load test; an excess of 200 psf in the transverseload test and 3494 pounds in the axial load wall test.

EXAMPLE 6 Structure with Polyurethane Fillet Picture Framing

Prepare a wall structure similar to the wall structure in Example 2except deposit the spray polyurethane foam as a triangular shaped beadaround the inside perimeter of the stud cavity and in the top ten inches(as measured from the top plate) of the stud cavity. The spraypolyurethane triangular cross section bead measures 1.5 inches by 1.5inches at the legs of the triangle, with one leg extending over thesheathing and the other leg extending over a stud, top plate or bottomplate. The volume of the stud cavity within ten inches of the top plateis filled to an expanded depth of 3.5 inches of polyurethane foam.

FIG. 2 illustrates a view of the Example 7 wall structure without theinterior sheathing and viewing from the interior side of the wallstructure. Wall structure 10 comprises 2×4 dimensional lumber studs 20that are 93 inches long between single 2×4 dimensional lumber top plate30 and single 2×4 dimensional lumber bottom plate 40 and spaced apart anominal 24 inches on center. The 2×4 dimensional lumber is 1.5 inchesthick and 3.5 inches wide. Exterior sheathing 50 is a sheet of one-inchthick STYROFOAM SIS™ Brand Structural Insulated Sheathing. Spraypolyurethane foam 60 extends around the interior perimeter of the cavityand fills the top ten inches within the cavity.

Test the wall structure in like manner as Example 2. The resulting wallstructure has a capacity of 699 pounds per lineal foot under the lateralload test, and (though not tested) is expected to achieve at least 4031pounds in the axial load wall test due to the similarity of thestructure to that in Example 2.

1. A light-framed wall structure comprising: (a) studs spaced apart fromone another in a range of nominally 16 to nominally 24 inches on center;(b) a bottom plate and a single top plate spanning the studs andattached to opposing ends of the studs such that the studs, top plateand bottom plate define a wall frame having opposing interior andexterior surfaces with the studs, top and bottom plate further defininga stud cavity within the wall frame, the stud cavity having a heightextending from bottom plate to top plate and a width extending from onestud to another stud; (c) sheathing spanning the width and height of thestud cavity and overlapping the studs and attached to at least one ofthe exterior and interior surfaces of the wall frame; and (d)polyurethane foam forming a seal around the inside perimeter of the studcavity and affixed to the sheathing material on at least one surface ofthe wall frame, the stud, top plate and bottom plate where thepolyurethane foam extends at least 1.5 inches over the sheathing, studs,top plate and bottom plate along the perimeter and further is present atan average thickness of at least 3.5 inches over the volume of the studcavity within six inches of the top plate; wherein the light-framed wallstructure is free of metal corner connectors or reinforcementscomprising a box-shaped section against which the studs, bottom plateand top plate abut.
 2. The light-framed wall structure of claim 1,wherein the studs are 2×4 dimensional building elements spaced apartfrom one another a nominal 24 inches on center.
 3. The light-framed wallstructure of claim 1, wherein the sheathing material is selected fromstructural insulated sheathing, rigid insulated sheathing and gypsumboard.
 4. The light-framed wall structure of claim 1, wherein thesheathing material is structural insulated sheathing.
 5. Thelight-framed wall structure of claim 1, wherein the polyurethane foamentirely covers any sheathing attached to at least one of the interiorand exterior surfaces of the wall frame that would otherwise be exposedwithin the stud cavity.
 6. The light-framed wall structure of claim 1,wherein the polyurethane foam has a thickness anywhere in the studcavity of at least one and one half inches thick as measuredperpendicularly from the sheathing material to which the polyurethanefoam is affixed.
 7. The light-framed wall structure of claim 1, whereinthe sheathing is exterior sheathing attached to the exterior surface ofthe wall frame.
 8. The light-framed wall structure of claim 7, furthercomprising interior sheathing spanning the width and height of the studcavity and overlapping the studs and attached to the interior surface ofthe wall frame.
 9. A light-framed wall structure comprising: (a) studsnominally spaced apart from one another 24 inches on center; (b) abottom plate and a single top plate spanning the studs and attached toopposing ends of the studs such that the studs, top plate and bottomplate define a wall frame having opposing interior and exterior surfaceswith the studs, top and bottom plate further defining a stud cavitywithin the wall frame, the stud cavity having a height extending frombottom plate to top plate and a width extending from one stud to anotherstud; (c) exterior sheathing spanning the width and height of the studcavity and overlapping the studs and attached to the exterior surface ofthe wall frame; and (d) polyurethane foam within the stud cavity andaffixed to the exterior sheathing material, studs, top plate and bottomplate defining the stud cavity, the polyurethane foam having an averagethickness of at least 0.5 inches within the stud cavity; wherein thelight-framed wall structure is free of metal corner connectors orreinforcements comprising a box-shaped section against which the studs,bottom plate and top plate abut.
 10. A process for making thelight-framed wall structure of claim 1, the process comprising thefollowing steps: (a) assembling studs spaced apart from one another in arange of nominally 16 to nominally 24 inches on center between a singletop plate and a bottom plate so as to form a wall frame having opposinginterior and exterior surfaces and defining a stud cavity between thestuds and top and bottom plates and affixing the studs to the top andbottom plates; (b) affixing sheathing to at least one of the exteriorand interior surfaces of the wall frame over the studs and stud cavity;and (c) disposing a polyurethane foam into the stud cavity so as to forma seal around the inside perimeter of the stud cavity that is affixed tothe sheathing material on at least one surface of the wall frame, thestuds, top plate and bottom plate defining the stud cavity, thepolyurethane foam being disposed in such an amount so as to have anaverage thickness of at least 3.5 inches in the stud cavity within sixinches of the top plate and extending at least 1.5 inches over thestuds, top plate, bottom plate and sheathing around the inside perimeterof the stud cavity; wherein the light-framed wall structure is free ofmetal corner connectors or reinforcement comprising a box-shaped sectionagainst which the studs, bottom plate and top plate abut.
 11. Theprocess of claim 10, wherein the studs are 2×4 dimensional buildingelements and they are assembled spaced apart from one another nominally24 inches on center.
 12. The process of claim 10, wherein the sheathingis selected from structural insulated sheathing material, rigidinsulated sheathing and gypsum board.
 13. The process of claim 10,wherein the polyurethane foam is a spray polyurethane foam and step (c)includes spraying the polyurethane foam into place.
 14. The process ofclaim 10, wherein polyurethane foam is disposed so as to entirely coverany sheathing attached to at least one of the interior and exteriorsurfaces of the wall frame that would otherwise be exposed within thestud cavity.
 15. The process of claim 10, wherein the polyurethane foamis disposed so as to have an average expanded thickness of at least 1.5inches within the stud cavity as measured perpendicularly from thesheathing to which the polyurethane foam is affixed.
 16. The process ofclaim 10, wherein the polyurethane foam is disposed to a greaterthickness proximate to the top plate than on average within the studcavity.
 17. The process of claim 10, comprises affixing sheathing toboth the exterior and the interior surfaces of the wall frame over thestuds and stud cavities.
 18. The process of claim 10, wherein the wallframe has multiple stud cavities defined therein by the studs, top plateand bottom plate and wherein step (b) includes affixing sheathing overmultiple stud cavities and step (c) includes disposing polyurethane asdescribed into multiple stud cavities.
 19. A building structurecomprising the light-framed wall structure of claim 1.